The present invention relates to relieving pull strain on electric power cords, and in particular to a special strain relief bushing design.
Strain relief bushings and open-closed bushings are commonly used at the connection of power cords and electrical leads to the body of an electrical device. Such bushings mount into openings in the housings of the devices to protect the conductor leads and can clamp the sheathing or insulation surrounding the conductor leads so that if the cord is pulled on the leads are not torn loose from the motor. Protecting the leads and relieving the strain on the leads reduces the chance that the electrical connection will be disrupted.
These bushings must perform sufficiently to satisfy national agency standards (such as United Laboratories), for example, regarding being irremovable from the device without tools and regarding the amount of pulling force they can sustain for a given time.
The bushings must clamp the cord to grip the sheathing sufficiently to meet these standards without excessively pinching the conductor leads. Consequently, the bushings must provide a properly sized opening for the cord. If the opening is too large, the bushing will not properly clamp the cord. If it is too small, it may pinch the conductors excessively. The chassis of the power cords can vary in size based on the number of conductors, the conductor gauge and the thickness of the sheathing required for particular applications. Thus, conventional bushings are made with various incrementally sized openings designed for use with cords of specific diameters. The need for numerous bushings for the various chord diameters can incur costly inventory and production expenses.
Accordingly, an improved universal bushing and cord retention system meeting industry standards is needed.